Process and apparatus for the manufacture of pulp



Feb. 20, 1934. c B, THQRNE 1,947,889

PROCESS AND APPARATUS FOR THE MANUFACTURE OF PULP Filed April 27, 1933\NVENTOR:

CARL B. THORNE' ATTORNEY.

Patented Feb. 20, 1934 *raoosss AND APPARATUS Fon 'imi MANUFACTURE orPULP Carl Busch Thorne, Hawkesbury, ohm-i0, Canada Application April 21,193:, Serial No. 668,209,

and in Ganada 8'Claims.

This invention relates to the manufacture of pulp and particularlyto animproved process and. apparatus therefor.

The object of the invention is to effect economics in the manufacture ofpulp by utilizing in an advantageous and convenient manner the heatcontained in the materials discharged from both the digester and-theblow pit.v a

Proposals have heretofore been made for the recovery of heat from thedigester relief gases but insofar as applicant is aware there are noprevious arrangements whereby full advantage may be taken of "all theheat available in treated pulp as well as in the relief gases and thepresent invention provides a simple practical method and apparatustherefor} ,The invention will now be described with reference to theaccompanying drawing, which illustrates in sectional elevation apparatusfor car-.

. Tying out the invention.

l'represents any suitable dige'ster as commonly used for cooln'ng woodchips in the manufacture ofsulphite pulp. 2 indicates any convenientrecipient or separator tank into which the relief acid from the digester1 is discharged through a pipe 3. In this tank the free gases areseparated from the liquor and the gases are led off along a pipe 4 whilethe liquor flows down through a pipe 5.

"6, 7- and 8 are heat exchang'ers consisting of a number of pipes madeof acid resisting material,

through which hot liquid or gas flows, these pipes Cold water, or otherliquid to being surrounded by a cooler liquid flowing in the oppositedirection, thus absorbing the heat from the pipes. The heat exchangersare of ordinary-construction and the'pipes are indicated only on theexchanger 8.

A blowpit 9 is provided and may conveniently be of the type commonlyused in pulp mills; that is, of the type comprising a tankhaving aperforatedfalse bottom 10; The pulp at a high temperature is dischargedfrom the idigest'er 1 into the blowpit 9 through the blowpipe 11controlled by a valve 12. The pulp is retained in theiblowpit 5 whilethe liquor drains downthrough the perforated false bottom 10 and passesthrough the pump 14 and pipe 15 to the heat exchanger 8. YA valve 16 isprovided in the pipe 15 and a discharge pipe 13' for wash water and thelike leads to the sewer. Gases liberated in the blowpit may be conveyedto a desired absorption or recovery? systemthrough pipe 29. l tbeheated, for example cooking liquor, is pumped under pressure into thetop of the heat exchanger 8 through a pipe 18 while the hot liquor fromthe blowpit 9'is April 20, 1932 (01f 92-7) w I pumped through the heatexchanger 8 in the bpposite direction. The cold liquid to be heatedflows over the outside of the exchanger pipes while the hot liquor is onthe inside in the known manner. The heat fromthe liquor is thustransferred to the cold liquid. The liquid from the heat exchanger 8passes through a pipe 19 to the heat exchanger 7 where it absorbs moreheat fronithe hot liquor which flowing through the heat exchanger f rom'therecipient 2. The liquor from the heat exchanger 7 is allowed to go tothe sewer. The water or other liquid from the exchanger '7 is carriedthrough the pipe 20 to-the exchanger 8 where it absorbs more heat fromthe gases from' the recipient 2 as wellas from the top'relief gases fromthe digester flowing through a pipe 21. The

liquid, which by this time will have reached a temperature of, say, to9. or more, as it leaves the heat exchanger 6, is carried through a Thegas from the heat exchanger 6 flows along a pipe 23 to any suitablerecovery tower or other apparatus as desired.

It may be very important when water is being heated in the heatexchangers, that the water should be free from any trace of acid, and insuch instances there must be no leakageof acid or gas out from the pipesinto the water. When it is necessary to accomplish this, the pressureoutside of the exchanger pipes is always kept 35 at a pressure which isgreater-than the pressure insidethepipesu In this way if there should beany break or leak in the pipes carrying thev acid, then the liquid willlead into the acid and not the acid into the water.

is placed in the water line 22 as it leaves the. last heat exchanger 6and this valve may be regulated so that. the pressm'e on the water in 6is higher than that of the hat fluids in the s s;

the system is always kept at a pressure which tem. A check valve 18' maybe provided in the supp y pipe 184:0 prevent reduction of'pressure inthe event of failure of the pump supplying no I I the liquid to beheated. I In addition to a thermostatically con trolled valve 25 mayalso be provided in,the

waterline 22, a.controlling thermometer 26 being placed in the heatexchanger 6. This valve 196 25 is of known constructionand may be setto'open at any desired temperature, for instance 90 to. 95 C., and willclose as soon as the temperature drops below this point.

In this way thepressure'of the water, as well l" i 00 To accomplishthis, apressure relief valve 24.

.pipe 22 to a tank, not shown, foruse as required. 75

as the temperature of the water, are controlled as desired.

In mills wherein the hot liquor is not drained .into a blowpit, the heatmay be recovered by means of an arrangement such as that indicated indotted lines to the right of Figure 1. In this case, the gas which isgiven ofi during cooking is relieved through the pipe 21', and theexcess cooking liquor is relieved through the pipe 3, as alreadydescribed. Now, instead of opening the valve 12 in the blowpipe 11 anddumping the whole charge of the digester into. the blowpit, a valve inthe pipe 21 is fully opened and the gas is allowed to escape through theheat exchanger 6 until .the pressure is reduced practically toatmospheric. A valve 15" in pipe 15 is nowopened. and,the liquor in thedigester is allowed to drain through a strainer bottom 35, through thepipe 15 and the heat exchanger 8 When all of the liquor has drained.ofi, then a water spray 36 is opened and the water washes the pulp inthe digester, the water descends and leaves the digester through thepipe 15 In this way the heat from the liquor is recovered in the heatexchanger 8. After the pulp is washed inside the digester, the valve 15is closed, and

the valve 12 in the pipe 11 is opened and'the pulp is allowed todischarge into the blowpit 9 or into any other tank for furtherprocessing in the mill. The liquid to be heated enters exchanger 8through a pipe 18 which may be fitted with a check valve 18", and,after, being heated in the exchanger, passes-on through pipe 19 toexchangers '7 and 6 to be further heated as hereinbefore described. Whenthis arrangement is employed the exchanger 8, and pipes 18 and 19 areomitted.

It will be apparent that the heat exchangers 6 and"? may be combined inone unit or that a larger number of heat exchangers may be used toobtain the same result. While the use of the separator 2 is preferred,it may be omitted and the gas and liquor together may pass through theheat exchangers.

I claim: 1. A process of manufacturing pulp, vwhich comprises cookingmaterials in a digester; passing fluids relieved from theupper part ofthe digester through heat exchanger means to recover heat therefrom,and, after the cooking operation has been completed, discharging solidsand liquids from the bottom of the digester into a blowpit, draining theliquids from said blowpit and passing them through. heat exchangingmenses 2. A process of manufacturing pulp, which comprises cooking-materialsin a digester, passing fluids relieved from the upper part ofthe digester through heat exchanger means to recover heat therefrom,and, after the cooking operation has been completed, discharging solidsand liquids from the bottom of the digester into a blowpit draining theliquids from said blowpit and passing them through heat exchangingmeans, circulating liquid to be, heated through said heat exchangingmeans in counter-current to the hot fluids from the digester, andautomatically maintaining the liquid to be heated at a higher pressurethan the fluids from the digester. Y

3. A process as claimed in claim 4, wherein the final temperature of theliquid to be heated is automatically maintained above a predeterminedfigure.-

e 4. A process of manufacturing pulp, which comprises cooking-materialsin a digester, discharging fluid from the upper part of the digester,separating the last mentioned fluids into liquid I and gaseouscomponents, passing said fluid components through separate heatexchangers, and,

after the cooking operation is complete, discharging solids and liquidsfrom the bottom of said digester into a blowpit, draining the liquidsfrom said blowpit and passing them through a heat exchanger, andcirculating liquid to be heat ed successively through said heatexchangers.

5. A process as claimed in claim 4, wherein the pressure of the liquidto be heated is automatically maintained above the pressure of the,fluids from the digester.

6. A process as claimed in claim 4, wherein if the final temperature ofthe liquid to be heated falls below a predetermined figure, thecirculation of the liquid to be heated is automatically stopped untilsaid predetermined temperature is again reached.

I 7. Apparatus for manufacturing pulp, comprising a'digester, a blowpithaving an outlet and a connection to said digester, heat exchangingmeans connected to said outlet, further heat ex- 12':-

changing means connected to the upper part of changing means.

8'. Apparatus as claimed in claim 7, wherein an automaticthermostatically controlled valve is provided to stop the circulation ofthe liquid to be heated when the temperature of said liquid falls belowa predetermined limit.

CARL BUSCH THORN'E.

